It was a long time ago so my memory is a bit fuzzy, but if I remember correctly it was fairly straightforward. It was right before and as SPF really became wort

It was a long time ago so my memory is a bit fuzzy, but if I remember correctly it was fairly straightforward. It was right before and as SPF really became worth doing. The thing that would get a lot of my customers running their own mail was the PTR not matching the name presented by the mail server and/or that name not being listed in the MX records for the domain it was relaying mail for. I did have to deal with the occasional IP that had been blacklisted on RBLs and that could be a pain the ass and typically the first order of business was actually blocking outbound SMTP except from their mail server. Those were the days that I don't miss.